Mine roof bolt tension indicator



1964 H. HARRISON 3,161,174

MINE ROOF BOLT TENSION INDICATOR Filed Aug. 6, 1965 2 SheetsSheet 1 ATTORNEYS Dec. 15, 1964 Filed Aug. 6, 1963 H. HARRISON 3,161,174

MINE ROOF BOLT TENSION INDICATOR 2 Sheets-Sheet 2 INVENTOR know //m4w/.s 0

ATTORNEYS United States Patent MINE RUUF BOLT TENSEGN HJDECA'EGEE Henry Harrison, Frost Creek Drive, Locust Valley, NSY. Filed Aug. 6, 1963, Ser. No. 3%,227 16 Claims. (Us 116-414) This invention relates to stress indicating devices, and has particular reference to a new and improved device for indicating when excessive stresses are imparted to a mine roof supporting bolts, and is a continuation-in-part of my copending application Serial No. 103,182, filed March 22, 1961, now US. Patent No. 3,104,645.

In the preparation of a mine tunnel for mining operations it is a common practice to reinforce the formation of rock above the mine roof. Conventional practice calls for drilling holes in the mine roof, and inserting bolts in the order of six feet or more in length into these holes. The bolts have an expansible anchor means on the end thereof inserted into the drilled hole, and are provided with a mounting plate which abuts against the mine roof. The bolt head is rotated, causing expansion of the anchor means against the interior of the drilled hole. Tension is imparted to the bolt by drawing up the bolt head in tight abutment with the lower surface of the mounting plate.

While this practice is widely used to bind a rock formation above a tunnel roof to inhibit the shifting of the rock, occassionally the rock formation will shift regardless of these bolts, causing grave danger to personnel working in the mine tunnel. In this regard, such a shift in the rock formation may result in a collapse of the mine tunnel roof. it is, therefore, imperative to have a positive and reliable means for ascertaining any shiftin the rock format-ion above the tunnel roof.

When the rock formation above the tunnel roof shifts, a resulting stress is placed upon the bolts which are located within the rock, the tensile stress imparted thereto being transferred to a bolt head generally secured to the end of the bolts which is visible from within the tunnel. Thus, by measuring this resulting increase of the stress imparted on the mine roof supporting bolt, a reliable means for indicating dangerous shifts in rock formations can be realized. Such means for indicating this shifting of rock formation will, of course, only be as reliable as the means for indicating the added stresses imparted to the bolt.

This problem has thus been appreciated in the prior art and numerous devices of varying degrees of reliability have been developed. Such devices are generally afiixed to the lower end of the bolt and olfer a means for indi cating adverse stresses which may be imparted to the bolt. Such prior art devices are generally quite expensive to manufacture and do not provide a totally reliable indicating means which readily indicates adverse bolt stresses Without a very careful observation of the relative position of the various parts. A truly efficient and practical indicating means should provide a. readily visible device which clearly shows dangerous stresses imparted to the bolt, with no necessity for careful measurement and observation.

This invention is accordingly directed to an improved device for indicating when excessive stresses are imparted to mine roof bolts in a simple readily observable manner, and in turn, indicating when dangerous shifts in the rock formations above the mine tunnel roof have taken place. Additionally, this invention approaches the mariner of measuring the added bolt stresses by a new and unusual means.

A primary object of the present invention is the provision of a bolt stress indicator'having means for indicating the'evidence of excessive tension on a mine roof sup porting bolt and means for indicating a loss of the desired amount of tension on the bolt.

ice

Another object of the invention is the provision of a bolt stress indicator in which the overload indicator comprises a flag that is carried on an overload pointer peg adjacent the bolt head and is arranged so that when the pointer peg becomes extruded to the point where it bends downwardly sufficiently upon an application of a predetermined amount of excessive tensile stress on the bolt, the flag is released from the peg and falls downwardly and in which the tension loss indicating means comprises a resilient clip carried in a stressed condition adjacent the bolt head and arranged to spring away from the bolt assembly upon the loss of a predetermined amount of stress on the bolt.

Yet another object of the invention is the provision of a device of the character described in which the overload indicating flag and the tension-loss indicating clip are joined by an elongated flexible element so that upon actuation of either indicator, that indicator will hang downwardly from the elongated flexible element attached to the non-indicating indicator to a point where it will be easily noticed by mine personnel.

A further object of the present invention is the provision of an indicator for indicating when the proper predetermined stress has been applied to a mine roof supporting bolt.

An additional object of the invention is the provision of a mine roof bolt shoe adapted to be preassembled on a mine roof bolt and carry a plurality of bolt stress indications.

lt is therefore an object of this invention to provide a bolt stress indicator which indicates excessive stress imparted to a bolt by an extrusion and resulting deflection of cantilevered flags disposed between the mine roof ceiling and the supporting bolt.

Another object of my invention is to provide a bolt stress indicator which includes means for extruding and deflecting cantilevered indicating means, when excessive stresses are imparted to the bolt.

Another object of my invention is to provide a bolt stress indicator which is of far simpler construction than those devices in the prior art, while affording a readily visible and inexpensive means for indicating when excessive stresses are imparted to a mine roof bolt.

Other objects and advantages of my invention will become apparent in the foregoing description and accompanying drawings, in which:

FEGURE 1 is a top plan view of the mine roof bolt assembly including the bearing plate and the indicator shoe with the indicators removed;

FIGURE 2 is an enlarged top plan view of an indicator shoe according to the invention illustrating the assembled position of the indicators.

FIGURE 3 is a reduced, exploded fragmentary perspective view of the mine roof bolt assembly including the indicators;

FIGURE 4 is a ectional view taken substantially along line 4-4 of FIGURE 1 showing the indicators in position on the indicator shoe;

FIGURE 5 is an enlarged perspective view of an initial tension indicator according to the invention;

FIGURE 6 is an enlarged perspective View of an overload pointer peg carrying an indicating flag; and

FIGURE 7 is an enlarged perspective view of a preferred spring wedge clip for use as a tension loss indicator.

In accordance with the novel features of this invention, there is provided an indicator shoe member having means mounted thereon for providing indication of the initial stress on the associated mine roof bolt, of subsequent excessive stress on the bolt, and of subsequent loss of stress on the bolt.

the aperture 34. 7 cold. forged from steel and may be casehardened for Referring first to FIGURE 4, a mine roof ll) is shown I having a long retaining bolt 12 disposed within a drilled hole 14. The bolt is engaged within the rock formation by a conventional expansible anchor 16 which includes an expansible shell sector 16a and an inner wedge 16b threaded onto the upper end of the bolt 12. The outer surface of .the shell sector 16a is provided with gripping serrations 16c.

Slidably mounted on the bolt 12 adjacent the roof 1d of the mine is an indicator assembly 20. The assembly 20 is located directly below an embossed bearing plate 22 having an upwardly projecting annular boss 24 which surrounds a large fluted hole 26 through theiplate 22,

the flutes 28 being for apurpose more fully described ing the preassembled indicator assembly is being secured in place in a mine roof. n V j The lower face of the shoe 30 has a downwardly facing generally rounded socket 38 formed therein surrounding Preferably the complete shoe 3%) is heavy duty applications. A protective coating such as tin or lead may be appliedtothe completed shoe. The socket '38 preferably receives a self-aligning ball-seat bearing 46.

which may be formed as an integral fillet on the head of the bolt 12.. The ball filletdll preferably is seated low in the ball socket 38 so that, when applied to amine roof havingan irregular surface, or in which an angled bolt hole has been inadvertently drilled so thatthe bolt de-. parts from perpe'ndicularity, up to about 12, will produce an error in the indicated tensions by the assembly of the invention of less than 8 percent. The fact that the indi cator shoe,"bearing plate and indicators according to this invention can be preassernbled on the bolt prior. to installing the bolt in the'mine means that the operation of inserting theindicating elements as discussed below is separated from the operation of installing the bolt, so that give an'indication of a predetermined amount of .stress on the mine roof bolt. As indicated in FIGURES 2 and 3, the indicator 52 is positioned on the upper surface of the shoe so that the peg 58 projects down a slot 42 and the tabs 56 are directed through the adjacent holes 48 and folded against the lower surface of the shoe. Thebody 54 of the indicator 52 is positioned so that its intermediate portion is intercalated between the bearing plate 22 and the raised extruding surface 44 adjacent the slot 42. As shown the pointer peg 58 is defined in part by a pair ofspaced slits 60 in the body 54 which extend to points near the radially inner edge of the body especially at the contoured portions 62 thereof. It has been found that. the amount of tension which will cause an indication by the peg 58 can be determined by the closeness of the contouredportions 62 to the slits 60. It can thus be seen that as the bolt 12-is turned home in the mine roof hole that the body of the indicator 52 will be squeezed between the plate 22 and the extruding surface 44.nntil the body is extruded to such a thinness along the line of extruding surface contact that the peg 58 turns down. By simple experimentation the configuration for indicators 52 can be found that will cause them to point downwardly to give the installer an indication of when the proper amount of initialtensionhas been applied to the bolt.

Now with greater regard to FIGURES 2, 3 and 6 the indicator assembly of the present invention also includes an overload te'nsion indicator 64 WhlCh' lS designed to provide a visible warning to mine personnel when the stress on a mine roof bolt has exceeded' a predetermined maximum at some time subsequent to the bolts installathan due to a roof. L

The indicator 64'wlu'ch is somewhat similar to the indicator. 52, includes an elongated body portion 66 having a pair of outwardly directed tabs. 68. thereon. A pointerpeg 70, defined by spaced slits" 72 extends transversely and downwardly from the intermediate portion of the body 66 so thatthe outer portion 74 of the peg lies in a plane generally lower than and parallel to that of the raminder of the body portion 66. Extending between the body 66 and the peg outer, portion 74 is a downwardly sloping portion 76 having a transversely directed .slot

shift in the rock formation comprising the V a 78 therethrough as'best illustrated in FIGURE 6, the slot 78 is adapted to slidingly receive the tab 80 of a flag 82,

so that the remainder of the flag is supported in a cantithe different. degrees of'skill and responsibility required 7 7 may be put in the hands of different personnel.

Referring to FIGURESl and 2, the shoe 3has two diametrically opposed elongated slots 42 formed there through near the outer periphery of the shoe so that the long axis of eachslot is generally perpendicular; to the radius of the shoe which pass through the center of the slot 42. Spaced radially inwardly from each slot 42 on the upper surface ofthe, shoe 30 is an elongated raised extruding surface i l which extends in a straight line 2 parallel with the slot 42 and mayadditionally extend diagonally inwardly therefrorn'at its outer ends .6. Adjacent each extruding surface outer end a hole 48 is formed through the shoe.

I A't le ast one elongated notch 507is formed as punching inthe peripheryofthe shoe '30 'between -thegtwo 1 elongated slots 42, for a giurpose that will be more fully described'below. l v I a a With particularregard to FIGURES 2 and 4, theindicator assembly o'f-the inventionin cludes an initial tension indicator 52 comprising an"'elong-ated'b0dy portion 54 having a tab 56 extending outwardly from each en dthereof. Intermediate the endsiof the body portion54 an integral transversely'extending downwardly stepped pointer peg158 .is formed ,so that the outer extent of the peg 58 lies ina plane, generallyparallel to that' of the body portion'.'l; The initial t nsion indicator is preferably levered fashion on the upper surface of the outer portion of the peg .58. The flag 82 may have a hole 83 formed therethroughto receive a ribbon for purposes more. fully describedhereinafter. The indicator 64 is assembled to the shoe 30, much-as is the indicator 52, by placing it on the upper surface of the shoe so that the transverse portion 76 extends down through a slot'42 and the peg outer 7 portion and flag, 82extend below and outwardly from the shoe 30. 1 The tabs 68' are directed downwardly through the adjacent, holes 48 and folded against the lower surface of the shoe 3%. Like the initial tension indicator 52, the overload tension indicator is positioned so that its body portion isintercalated between the lower surface of the bearing plate and, the raised extruding surface 44 adjacent the associatedslot 42.. The width, composition and configuration of the-overload pointer peg are such that the peg will be'extruded to a thinness such that it will turn downward sharply upon the application of an overload tensile stress of apredeterminedmagnitude to the bolt as by a shifting of the rock' s'trata forming themine roof. When this occurs the generally horizontal;

"outer peg portion 74 in tilting downwardly will no longer provide'support for the flag 82 and consequentlythe flag 8 will fall from the assembly to provide the desired visual indication of adverse tensile stress on the associated mine roofv bolt.

formed from-a relatively. 'softimaterial such as aluminum and the. body portion; has a width and coniiguration to "In FIGURES, 2, 3,14 and 7 aterna ism of the novel's'pring wedgecliptension loss indicator 84 is shown. The cli p .84 comprises a generally resilient strip of metal such as strapping steel that has been formed into a triangular shape including a short leg and two long legs. The short leg 86 preferably has the transverse edges thereof turned downwardly as shown in FIGURE 4, to form a wedge, one long leg 88 extends angularly from the leg 86 and reverses to form a free leg 90 which has its outer end adjacent that of the wedge leg 86 when at rest as shown in FIGURES 3 and 7 but may be resiliently biased toward the juncture of the wedge leg and the leg 88 as shown in FIGURES 2 and 4.

The spring wedge clip is joined to the indicator assembly by inserting the wedge 86 between the shoe 30 and the plate 22 adjacent a notch 50 so that the leg 90 is resiliently biased to its loaded position by abutting the periphery of the shoe 30 at the notch 50. If at any time after the predetermined tensile stress has been put on the bolt 12, as indicated by the indicator 52, the rock strata should shift so that the tension on the bolt is lowered below a predetermined value the plate 22 will elastically partially recover its original shape and move with respect to the shoe 30 to a degree such that the wedge 88 will be loosened enough that the leg 90 will be able to push the clip away from the assembly to provide the desired visible indication of critical tension loss to the mine personnel.

As best shown in FIGURES 2, 3 and 4 the spring wedge clip and overload tension indicating flag are preferably joined to one another by an elongated flexible element such as a pleated ribbon 92. Therefore, when either of these indicators is actuated by an abnormal tension condition, so that the indicator falls away from the assembly, it will hang suspended on the ribbon supported by the other indicator. Experimentation has shown that indicators suspended in this manner will be more readily seen by mine personnel that are indicators which merely bend and must be observed closely to determine their condition or ones which indicate by falling to the mine floor where they may lie unobserved among debris or the like. A pleated ribbon is preferred for connecting the indicators because the pleats will allow the ribbon to be stored compactly in the assembly, yet extend to a greater length under the weight A of a detached indicator. In this regard it should be understood that the exact configuration of the indicators shown are merely the preferred forms, it being within the purview of the invention that some modifications are possible such as adding weights to the indicators so that they will more easily unfold the pleated ribbon when they begin to indicate the abnormal tension condition.

As seen especially in FIGURES 2 and 4 the radially inner side of the extruding surfaces 44 are milled to be smoothly convex while the outer side is sharply relieved. Therefore, the contour of each extruding surface as viewed in section (FIGURE 4) is quite unsymmetric. This configuration tends to provide extrusion of the associated pointer peg or initial tension indicator in one direction only, and also causes it to curl much as the rapid rate of growth on one side of a vine causes the vine to curve in the direction opposite from the fast growing side.

When the indicator assembly depicted in FIGURE 3 is assembled as shown in FIGURES 2 and 4 so that the bolt head is drawn up to the desired tension, compressive stress is placed on the initial stress indicator 52 and the overload pointer peg 58. The capacity of these indicators to withstand extrusion can be controlled, in addition to the ways discussed above, bythe shape of the extruding surfaces. The amount of stress required to extrude an indicator where a knife-edge extruding surface is used is considerably less than the stress required where an arc-shaped extruding surface of a relatively large radius is utilized.

When a circular cylindrical extrusion surface is provided on the extruding member, extrusion begins at a certain bearing force; and, if that force is maintained the indicator is pinched down to a very small thickness-too small to support the force of gravity on the cantilevered indicator. During the extrusion process the thickness of extruding metal decreases, so that an increased pressure is required to force it out. The width of bearing of the cylindrical surface against the flag also decreases, how ever, as the thickness decreases, so that the total bearing force required to extrude the flag is substantially constant. The amount of bearing force required to cause extrusion is generally proportional to the radius of curvature of the cylindrical surface of the extruding member.

When the extruding member has an obtuse or acute angled edge pressing into the indicator, the bearing force necessary to cause extrusion diminishes rapidly as the thickness of metal decreases. On the other hand, when it has a parallel fiat bearing surface, the bearing force increases rapidly with reduction of the squeezed metal thickness. Between these two extremes, the surface of the extruding member can be shaped to give any desired intermediate relation between bearing force and thickness of squeezed-out metal.

The force at which extrusion takes place depends primarily on three factors: It is, as already noted, directly proportional to the radius of curvature of the extruding member; it is directly proportional to the width of the indicator; and it is approximately proportional to the maximum yield strength of the material, in shear. For example, an indicator of SAE 3003 aluminum alloy, three inches wide, pressed by extruding members having a radius of curvature of inch, is extruded by a force of about 16,000 pounds. A low carbon steel indicator of the same size, under the same conditions, supports about 56,000 pounds. The thickness of the indicator before assembly and its initial condition of work hardening do not effect the total force at which extrusion takes place.

As already stated, the compressive stress in the indicator which must be withstood by the parts between which it is squeezed, increases as the thickness decreases, and may reach very high values. When an indicator is extruded and bends or curls to make an indication of excessive bolt stress, its thickness is reduced to less than .003 inch. This corresponds to compressive stress of about 100,000 psi. An indicator of low carbon steel under similar geometrical conditions would have an internal compressive stress of over 300,000 p.s.i.

it has been found that friction at the boundary of the indicator material may cause a variation in extruding force in the order of il0%. To control this variable, and also to combat corrosion in the warm, humid conditions frequently found in mines, the parts of this device may be coated with grease at the time of assembly so long as care is taken to insure that the grease will not interfere with the dropping of the flag 82, the expulsion of the spring wedge clip or the unfolding of the ribbon.

Since the extruding operation moves the indicator material outward at the same time its thickness is reduced, the section of the flag becomes more or less wedge shaped, with the thinnest portion of the wedge'where the extruding surface 44 is closest to the mounting plate 22. it has been found that the portion of the iiag material adjacent the hearing plate extrudes more rapidly than the portion adjacent the shoe, so that the iiag tends to curl away from the hearing plate.

In assembling the bolt stress indicator assembly the initial stress indicator and overload stress indicator are first attached to the indicator shoe as discussed above. The self-aligning bearing is then slid on the bolt followed by the indicator shoe 3-0 and the plate 22. The shoe 30 is then rotated until it seats in the fluted opening of the plate 22. After an appropriate hole has been drilled in the formation above the mine tunnel roof, a perpendicular spot-face surface may be bored at the open end of the hole. In instances where the hole is accurately drilled and spot-faced it is within the purview of the invention that the structure of the indicator shoe, ball fillet and bolt head can all be consolidated in the bolt head so that the indicators are all carried directly by the bolt head immediately subjacent the bearing plate. In any event after the roof hole has been drilled the shaft of the bolt is then mine personnel.

Z properly inserted into the hole and the tension loss indicating spring wedge clip put into place and held as the bolt is turned home in the hole. The anchoring shell is expanded by the rotation of the bolt head as the bolt is tensioned. During this tightening the extruding surfaces sink slightlyinto the indicators until they support the load. When the proper predetermined tension has been reached the initial tension indication will "be de flected downwardly due to extrusion thereof. v

If afterassembly the bolt should be subjectedito increased stress beyond a predetermined level resulting from a shift of the rock formation, the stress will be imparted to the overload indicator pointer peg 64 causing a downa ward deflection thereof by extrusion so that its flag 82 slides out and hangs by the pleated ribbon from the spring wedge clip. a v

Alternately, if the bolt should be subjected to a loss of stress to a predetermined degree resulting from a sense and accordingly theextentof'this invention should be limited only by the spirit and'scope of the claims, ape

pended hereto. 7

What is claimed is: g 1. In a mine roof boltassernbly having an elongated bolt with an expansible anchoring means at its'one end adapted for insertion in an upwardly extending hole in a mine roof with anchoring means end foremost, the other end of said bolt having head means thereon, the combi nation comprising: a bearing plate carried by said bolt adjacent the mine roof; first means'carried by thebolt between the bearing plate and the bolt head for providing a visual indication of the application of tensile stress respect to the bolt head to" accommodate the bolt assemtween the bearing plate and the bolt head for providing a visual indication of the application of tensile stress above a predetermined value to the'bolt; the first indicating means'comprising ametallic strip having a free end extending generally horizontally and outwardly from the bolt and arranged to be bent downwardly by stress induced movement-of the bolt and head toward the bearing plate; and second means carried by the bolt between the bearing plate and the bolt head for providing a visual indication of the lowering of tensile stress incident on the 0 bolt below a predetermined value; and additionally comprising a third indicating means, similar to the first, including a strip of vmetal carried in a cantilevered fashion between the bolt head and the bearing plate and arranged to be bent downward appreciably by the movement of the bolt head toward thebearing'plate as the bolt is turned home in the mine roof hole thereby providing a visual indication when the proper predetermined tensile stress has been applied to the bolt. 7

7; Ina mine roof bolt assembly havingan elongated bolt with an expansible anchoring means at its one end adapted for insertion in an upwardly extending hole in a mine roof with i anchoring .means end foremost, the other end of said bolt having head means thereon, the combination comprising: ab'earing plate carried by said bolt adjacent-the mine roof; first means carried by the bolt be.-

' tween the bearing plate and the bolt head for providing a visual indication of. the application of tensile stress above a predetermined value to'the bolt; the first 'indi- 1 extending generally horizontally and outwardly from the bolt and arranged to be bent downwardly by stress in duced movement of the bolt headto-ward the bearing eating means comprising a metallicstrip having a free end plate, and including an overload tension indicating flag {means carried by the bolt between the bearing plate and the bolt head -for providing a visual indicationof the lowering of tensile stress incident on the bolt below a predetermined value; means interposed between the bolt head and the bearing plate forsupporting the first and second indicators in a cantilevered fashion, said last-menengagedbetween the bearing plate and the indicator'shoe for providing a visual indication of thelowering of tensile 7 stress incident on the boltbelow a predetermined value,

the second indicating means including a pre-loaded wedge adapted to pop out and fall 'awayfrom the bolt upon thernovement of "the bolt head away from the. bearing plate overload tensionindicating flag to theztension loss indi-iv by a predetermined amount, thereby indicating a lossot eating wedge whereby when one of the indicators is actuated and separates from the bolt assembly it will remain suspended by the elongated flexible element from the nonactuated indicator in positionfor easy observation" by 3. A combinationasset forth in elaim 2 wherein the 1 elongated flexible element is a pleated ribbon.

4. The combination set forth in claim 3v additionally including means interposed between the bolt head andthe bearingplate for supporting; the first and second indi cators in a cantilevered fashion.

' by the bolt between the bearing plate and the bolt head "for providing a visual indication of the lowering of tensile stress incident on the bolt below, a predetermined andincluding a resiliently biased clip contacting the in: dicator shoe whereby when the bolt head moves away i from the bearing plate the clip pushes the wedge out from between the bearinglplate and the indicator shoe.

' 8'. Acombination as set forth in claim 7 wherein the metallic strips comprising theiirstand'third indicators are composed essentially/oi? aluminum and theitension loss indicating wedge: and clipare integrally composed of strapping steel. ,7

'9. In a mine roof .bolt assembly having an elongated bolt with an .e'xpan sible anchoring, means at its one end adapted for insertion in an upwardly extending hole in a rnine roofwithanchoring means foremost, the other end of said bolt havingzhead means thereon, the combination comprising: a bearing plate carried. by said bolt adjacent the mine roof; first means carried by the bolt between the determined value to the bolt; and second means carried valueameans interposed between thebolt headand the bearing plateforfsupporting the first and second indicators N in cantileveredfashiorfz, the last men'tione dmeans' including an annular'indicatorshoegcarriedjby the bolt for angular movement with respect to the bolt head to accommodate the bolt assembly to uneven mine roofs; said bearing plate having stop means thereon for engaging said indicator shoe to prevent the rotation of the shoe with respect to the bearing plate during the insertion of the bolt in a mine roof hole whereby the first and second indicators, the indicator show and the bearing plate can be pre-positioned on the bolt prior to said insertion.

10. The combination set forth in claim 9 wherein the bearing plate stop means comprises means defining a non-- circular opening through the bearing plate and the in dicator shoe includes at least one raised portion thereon for engagement with the non-circular bearing plate open mg.

11. The combination set forth in claim 10 wherein said bearing plate includes a substantial raised annular boss thereon surrounding the bolt whereby the first and second indicators are protected from accidental contact by mine personnel and equipment.

12. In a mine roof bolt assembly having an elongated bolt with an expansible anchoring means at its one end adapted for insertion in an upwardly extending hole in a mine roof with anchoring means end foremost, the other end of said bolt having head means thereon, the combination comprising: a bearing plate carried by said bolt adjacent the mine roof; first means carried by the bolt between the bearing plate and the bolt head for providing a visual indication of the application of tensile stress above a predetermined value to the bolt; and second means carried by the bolt between the bearing plate and the bolt head for providing a visual indication of the lowering of tensile stress incident on the bolt below a predetermined value, said second indicating means including a pre-loaded wedge adapted to pop out and fall away from the bolt upon the movement of the bolt head away from the bearing plate by a predetermined amount, thereby indicating a loss of tensile stress incident on the bolt.

13. A combination as set forth in claim 12 additionally including an elongated flexible element connecting the overload tension indicating flag to the tension loss indicating wedge whereby when one of the indicators is actuated and separates from the bolt assembly it will remain suspended by the elongated flexible element from the non-actuated indicator in position for easy observation by mine personnel.

14. A combination as set forth in claim 13 wherein the elongated flexible element is a pleated ribbon.

15. The combination set forth in claim 14 additionally including means interposed between the bolt head and the bearing plate for supporting the first and second indicators in a cantilevered fashion.

16. The combination set forth in claim 15 wherein the indicator supporting means comprises an annular indicator show carried by the belt for angular movement with espect to the bolt head to accommodate the bolt assembly to uneven mine roofs.

Lanius Jan. 8, 1963 Harrison Sept. 24, 1963 

1. IN A MINE ROOF BOLT ASSEMBLY HAVING AN ELONGATED BOLT WITH AN EXPANSIBLE ANCHORING MEANS AT ITS ONE END ADAPTED FOR INSERTION IN AN UPWARDLY EXTENDING HOLE IN A MINE ROOF WITH ANCHORING MEANS END FOREMOST, THE OTHER END OF SAID BOLT HAVING HEAD MEANS THEREON, THE COMBINATION COMPRISING: A BEARING PLATE CARRIED BY SAID BOLT ADJACENT THE MINE ROOF; FIRST MEANS CARRIED BY THE BOLT BETWEEN THE BEARING PLATE AND THE BOLT HEAD FOR PROVIDING A VISUAL INDICATION OF THE APPLICATION OF TENSILE STRESS ABOVE A PREDETERMINED VALUE TO THE BOLT; THE FIRST INDICATING MEANS COMPRISING A METALLIC STRIP HAVING A FREE END EXTENDING GENERALLY HORIZONTALLY AND OUTWARDLY FROM THE BOLT AND ARRANGED TO BE BENT DOWNWARDLY BY STRESS INDUCED MOVEMENT OF THE BOLT HEAD TOWARD THE BEARING PLATE, AND INCLUDING AN OVERLOAD TENSION INDICATINTG FLAG SLIDABLY SUPPORTED ON THE UPPER SURFACE OF THE METALLIC STRIP AND ARRANGED TO FALL THEREFROM UPON THE DOWNWARD BENDING OF THE METALLIC STRIP; AND SECOND MEANS CARRIED BY THE BOLT BETWEEN THE BEARING PLATE AND THE BOLT HEAD FOR PROVIDING A VISUAL INDICATION OF THE LOWERING OF TENSILE STRESS INCIDENT ON THE BOLT BELOW A PREDETERMINED VALUE, THE SECOND INDICATING MEANS INCLUDING A PRE-LOADED WEDGE ADAPTED TO POP OUT AND FALL AWAY FROM THE BOLT UPON THE MOVEMENT OF THE BOLT HEAD AWAY FROM THE BEARING PLATE BY A PREDETERMINED AMOUNT, THEREBY INDICATING A LOSS OF TENSILE STRESS INCIDENT ON THE BOLT. 